Device for cutting of glass sheet

ABSTRACT

Disclosed herein is a device for cutting a glass sheet, continuously supplied after a melting and solidification process, into quadrangular glass substrates. The glass sheet cutting device includes two or more cutters for cutting a glass sheet into quadrangular glass substrates, a defect inspector for scanning the glass sheet to three-dimensionally check defect positions in a length direction, a width direction and a thickness direction of the glass sheet, a position adjuster for moving at least one of the cutters to a portion of the glass sheet at which few defects are distributed, and a controller for informing the position adjuster of positions of the cutters based on the scanned results received from the defect inspector.

TECHNICAL FIELD

The present invention relates to a glass sheet cutting device, and, moreparticularly, to a device for cutting a glass sheet, continuouslysupplied after a melting and solidification process, into quadrangularglass substrates, the glass sheet cutting device including two or morecutters for cutting a glass sheet into quadrangular glass substrates, adefect inspector for scanning the glass sheet to three-dimensionallycheck defect positions in a length direction, a width direction and athickness direction of the glass sheet, a position adjuster for movingat least one of the cutters to a portion of the glass sheet at which fewdefects are distributed, and a controller for informing the positionadjuster of positions of the cutters based on the scanned resultsreceived from the defect inspector.

BACKGROUND ART

Recently, flat panel displays, such as a liquid crystal display (LCD), aplasma display panel (PDP), and an organic light emitting diode (OLED)have attracted considerable attention.

Glass substrates used to manufacture such flat panel displays aremanufactured through a molding process of molding glass molten in aglass smelting furnace in the form of a flat panel and a cutting processof cutting the flat glass panel according to a primary standard. Themanufactured glass substrates are transferred to a processing line inwhich the glass panels are processed. In the processing line, the glasssubstrates are cut to sizes suitable for the standard of desired flatpanel displays, and sharp edges of the glass substrates are ground.Also, quality of the glass substrates manufactured in the processingline is inspected using an inspector to determine whether the glasssubstrates have defects. If the glass substrates have defects, the glasssubstrates are destroyed. If the glass substrates have no defects, theglass substrates are shipped as finished products.

Meanwhile, the glass substrates may have defects, such as bubbles,foreign matter, for example stone particles, contamination, scratches,cut chips, and cracks, due to various causes during such a series ofmolding, cutting and grinding processes of the glass substrates asdescribed above. For this reason, in order to manufacture high-qualityflat panel displays, defects of the glass substrates are inspected tosort the glass substrates into good-quality products and defectiveproducts, and reasons of defects caused during the manufacturing processare checked and corrected.

Glass substrates are inspected through macrography and opticalinspection using a camera and a microscope. Also, the glass substratesare totally inspected, and then some of the inspected glass substratesare sampled so as to secure accuracy and reliability of the inspection.

The macrography to inspect defects of the glass substrates is generallyperformed at an inspection station installed separately from a transferline of the glass substrates. An inspector unloads a glass substratefrom the transfer line and loads the unloaded glass substrate to theinspection station using a handler, and inspects defects of the glasssubstrate using a lighting device, such as a fluorescent lamp or ahalogen lamp, provided in the inspection station. However, the glasssubstrate may be scratched or cracked due to physical contact and shockduring loading and unloading of the glass substrate using the handler.Also, a lot of time is needed, thereby reducing productivity. Inparticular, it is increasingly difficult to handle glass substrates dueto the increase in size and the decrease in thickness of the glasssubstrates. For this reason, it takes much time and manpower to inspectthe glass substrates.

Consequently, there is a high necessity for a glass sheet cutting devicethat scans a glass sheet to three-dimensionally check defect positionsof the glass sheet in the length direction, the width direction and thethickness direction of the glass sheet during a continuous cuttingprocess and cuts the glass sheet into various kinds of glass substrates,thereby lowering a defect rate, preventing waste, and reducingmanufacturing costs.

DISCLOSURE Technical Problem

Therefore, the present invention has been made to solve the aboveproblems, and other technical problems that have yet to be resolved.

Specifically, it is an object of the present invention to provide aglass sheet cutting device configured so that, when a glass sheet is cutinto glass substrates, the glass sheet is scanned using the defectinspector to three-dimensionally check defect positions in the lengthdirection, the width direction and the thickness direction of the glasssheet, and at least one of the cutters is moved to a portion of theglass sheet at which few defects are distributed to manufacture aplurality of glass substrates, thereby maximizing yield of the glasssubstrates.

Also, it is another object of the present invention to provide a glasssheet cutting device for cutting a glass sheet into at least two kindsof glass substrates, thereby improving yield of the glass substrates andreducing manufacturing costs.

Technical Solution

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a device forcutting a glass sheet, continuously supplied after a melting andsolidification process, into quadrangular glass substrates, the glasssheet cutting device including two or more cutters for cutting a glasssheet into quadrangular glass substrates, a defect inspector forscanning the glass sheet to three-dimensionally check defect positionsin a length direction, a width direction and a thickness direction ofthe glass sheet, a position adjuster for moving at least one of thecutters to a portion of the glass sheet at which few defects aredistributed, and a controller for informing the position adjuster ofpositions of the cutters based on the scanned results received from thedefect inspector.

The glass sheet cutting device according to the present invention scansa glass sheet to three-dimensionally check defect positions in thelength direction, the width direction and the thickness direction of theglass sheet, moves at least one of the cutters to a portion of the glasssheet at which few defects are distributed, and cuts the glass sheetinto quadrangular glass substrates. Consequently, it is possible toefficiently manufacture glass substrates during a continuousmass-production process while minimizing a defect rate of the glasssubstrates.

Also, the defect inspector three-dimensionally checks defect positionsof the glass sheet to decide positions of the cutters. Consequently, itis possible to properly move the cutters based on the defect positionsand to perform a continuous cutting process.

The kind of the cutters is not particularly restricted so long as thecutters have a structure or characteristics to cut the glass sheet intoquadrangular glass substrates. A representative example of each of thecutters may be a diamond knife or a light source for cutting, such as alaser.

In a preferred example, the cutters may include a first cutter forcutting the glass sheet in the width direction (‘Y direction’) intofirst glass substrates, a second cutter for cutting each of the firstglass substrates in the length direction (‘X direction’) into secondglass substrates, a third cutter for cutting each of the second glasssubstrates in the width direction (‘X direction’) into third glasssubstrates, and a fourth cutter for cutting the third glass substratesin the length direction (‘Y direction’).

For example, the first cutter may be moved to a portion of the glasssheet at which few defects are distributed in the length direction (‘Xdirection’) to cut the glass sheet into the first glass substrates,thereby improving yield of the first glass substrates.

For example, the second cutter may cut each of the first glasssubstrates into second glass substrates having no defects when each ofthe first glass substrates has no defects, thereby easily manufacturinggood-quality second glass substrates. The size of each of the secondglass substrates may be decided based on, for example, productspecifications.

For example, the third cutter may cut each of the second glasssubstrates into a third glass substrate having defects and a third glasssubstrate having no defects when each of the second glass substrates hasdefects.

For example, the fourth cutter may cut the third glass substrate havingdefects to remove the defects from the third glass substrate, therebyeasily manufacturing good-quality fourth glass substrates. The size ofeach of the fourth glass substrates may be decided based on, forexample, product specifications.

In a preferred example, the fourth cutter may cut the third glasssubstrate having defects from one end or opposite ends of the thirdglass substrate within a range of less than 30% of the length of thethird glass substrate to remove the defects from the third glasssubstrate. More preferably, the portion of the third glass substratehaving defects extends from one end or opposite ends of the third glasssubstrate within a range of 0.1 to 30% of the length of the third glasssubstrate.

Meanwhile, among the third glass substrates, a defective glass substratehaving defects located at a portion that cannot be removed by the fourthcutter may be destroyed.

In the above structure, the width of the defective glass substrate maybe 20% or less, preferably 0.1% to 20%, of the size of the glasssubstrate having no defects to minimize the size of the defective glasssubstrate.

Meanwhile, the defect inspector may be disposed ahead of the cutters,preferably, in the length direction of the glass sheet. Consequently, aninspection process is performed before the cutters cut the glass sheet,thereby greatly improving yield as compared with a conventional glasssheet cutting device that performs an inspection process after cuttingthe glass sheet.

In particular, the characteristic of the defect inspector forthree-dimensionally checking defects of the glass sheet in considerationof the thickness direction (Z direction as well as the length direction(X direction) and the width direction (Y direction) of the glass sheetduring the inspection process of inspecting the defects of the glasssheet is a novel concept that can be seen from the conventional glasssheet cutting device.

In a preferred example, the defect inspector may include two or morecameras for checking the defect positions of the glass sheet in thelength direction, the width direction and the thickness direction of theglass sheet. The number of the cameras may be varied depending upon thewidth of the glass sheet. Preferably, the defect inspector includes 2 to30 cameras.

The cameras may measure distances and angles between the cameras and thedefects to check the defect positions. Specifically, the defectinspector includes two or more cameras to three-dimensionally measureangles and straight distances between the cameras and each defect.Consequently, it is possible to accurately check position coordinates(X, Y, Z) of each defect using the measured angles and straightdistances.

The defects may occur in various forms. For example, the defects mayinclude fish eyes, bubbles, black dots, white dots, or protrusions orgrooves formed at the outer surface of the glass sheet.

Meanwhile, the defects located at the outer surface, i.e. the top orbottom, of the glass sheet are excluded from objects to be cut. Forexample, defects located at the top or bottom of the glass sheet may beremoved by grinding during a post processing process. Consequently, thedefects are excluded from objects to be cut, thereby improvingproductivity. According to circumstances, only defects located at thebottom of the glass sheet may be removed by grinding during the postprocessing process, and defects located at the top of the glass sheetmay be sorted as objects to be cut.

In a preferred example, the controller may include an arrangement serverfor performing mixed integer linear programming based on positionalinformation of the defects input by the defect inspector to imaginarilyarrange glass substrates on the glass sheet. Consequently, it ispossible to set a plan for optimally arranging glass substrates with therespect to a glass sheet.

For example, in the mixed integer linear programming, restrictiveconditions may include X, Y, Z coordinates of defects, the kind and sizeof a glass substrate, and the size of a glass sheet, and an objectivefunction may be set to maximize space utilization of the glasssubstrate.

In a concrete example, a mixed integer linear programming model may bedefined as follows.

$\begin{matrix}{{Objective}\mspace{14mu} {function}\text{:}\mspace{14mu} {Maximize}\mspace{14mu} {\sum\limits_{k}{L_{k} \times H_{k} \times Z_{k}}}} & {{Expression}\mspace{14mu} (1)}\end{matrix}$

Restrictive Conditions:

X _(k2) =X _(k1) +L _(k)   Expression (2)

Y_(k2)=Y_(k1)   Expression (3)

X_(k3)=X_(k1)   Expression (4)

X _(k3) =Y _(k1) −H _(k)   Expression (5)

X_(k4)=X_(k2)   Expression (6)

Y_(k4)=Y_(k3)   Expression (7)

−M×(2−Z _(k) Z _(k′))+X_(k2) ≦X _(k′1) +M×(1−ZZ _(kk′1))   Expression(8)

−M×(2−Z _(k) −Z _(k′))+X _(k′2) ≦X _(k1) +M×(1−ZZ _(kk′2))   Expression(9)

M×(2−Z _(k) −Z _(k′))+Y _(k1) ≧Y _(k′3) −M×(1−ZZ _(kk′3))   Expression(10)

M×(2−Z _(k) −Z _(k′))+Y _(k′1) ≧Y _(k3) −M×(1−ZZ _(kk′4))   Expression(11)

Definition of Variables:

-   -   Z_(k): 1 or 0 if a quadrangle k is valid    -   ZZ_(kk′m): Positional relationship between two quadrangles k and        k′ (m=1, 2, 3, 4)    -   X_(kn): X coordinate of a defect n of a quadrangle k (n=1, 2, 3,        4)    -   Y_(kn): Y coordinate of a defect n of a quadrangle k (n=1, 2, 3,        4)    -   k: A set of all quadrangles having defects    -   L_(k): Length of a quadrangle k    -   H_(k): Height of a quadrangle k    -   M: Very large number to express validity of 0-1 variables

In the above model, Expression (2) to Expression (7) are restrictiveconditions to show positional relationships between for corner points ina quadrangle k, and Expression (8) to Expression (11) are restrictiveconditions to show positional relationships between two quadrangles kand k′.

Here, m=1 means that the quadrangle k is located at the left side of thequadrangle k′ and m=2 means that the quadrangle k is located at theright side of the quadrangle k′. Also, m=3 means that the quadrangle kis located at the upper side of the quadrangle k′ and m=4 means that thequadrangle k is located at the lower side of the quadrangle k′. M is avariable to exclude an infeasible solution from the mixed integer linearprogramming

However, the above-mentioned mixed integer linear programming model isan illustrative example. Those skilled in the art to which the presentinvention pertains can set various mixed integer linear programmingmodels based on the disclosure of the present invention, and therefore,the scope of the present invention is not limited to the illustrativeexample.

According to circumstances, the glass sheet cutting device may furtherinclude a thickness inspector for checking unevenness of the outersurface of the glass sheet. In a concrete example, the thicknessinspector may include a sensor. Consequently, it is possible to measurean index of refraction of the glass sheet when light is transmittedthrough the glass sheet and to check unevenness of the outer surface ofthe glass sheet based on the measured index of refraction.

In a preferred example, if the unevenness of the outer surface of theglass sheet is 1% or more of the thickness of the glass sheet, theunevenness may be regarded as defects to be removed.

That is, if the unevenness of the outer surface of the glass sheet is 1%or more of the thickness of the glass sheet, it is not possible toobtain a good-quality glass sheet by grinding. For this reason, theunevenness is regarded as defects to be removed, thereby improving aquality rate of glass substrates.

In another preferred example, the thickness inspector may be positionedbetween the defect inspector and the cutters. Consequently, it ispossible to measure the coordinates of defects using the defectinspector and, in addition, to check defects due to the unevenness ofthe glass sheet using the thickness inspector, thereby improving aquality rate of glass substrates.

The glass substrates are not particularly restricted so long as theglass substrates can be used to manufacture flat panel displays.Preferably, each of the glass substrate is a glass panel for liquidcrystal displays (LCDs), a glass panel for organic light emitting diodes(OLEDs) or a glass panel for plasma display panels (PDPs).

On the other hand, the glass sheet cutting device may include a firstproduction line to produce relatively large glass substrates, from whichdefects have been removed and a second production line to producerelatively small glass substrates, from which defects have been removed.

The second production line may diverge from the first production line sothat good-quality products and defective products can be easily divided.

In accordance with another aspect of the present invention, there isprovided a glass substrate manufacturing method. In a concrete example,there is provided a method of manufacturing quadrangular glasssubstrates from a glass sheet, which is continuously supplied after amelting and solidification process, the glass sheet manufacturing methodincluding an inspection process of scanning the glass sheet using adefect inspector to three-dimensionally check the positions of defectsin a length direction, a width direction and a thickness direction ofthe glass sheet, a first division process of cutting the glass sheet inthe width direction (‘X direction’) using a first cutter to divide theglass sheet into first glass substrates, a second division process ofcutting each of the first glass substrates in the length direction (‘Ydirection’) using a second cutter to divide each of the first glasssubstrates into second glass substrates, a third division process ofcutting each of the second glass substrates in the width direction (‘Xdirection’) using a third cutter to divide each of the second glasssubstrates into third glass substrates, a fourth cutting process ofcutting each of the third glass substrates in the length direction (‘Ydirection’) using a fourth cutter, and a post processing process ofgrinding surfaces of glass substrates obtained in the fourth cuttingprocess to remove defects that have been sorted as ones that can beremoved in the inspection process.

For example, the good-quality second glass substrates obtained throughthe second division process may be glass substrates for large-sizedLCDs, the good-quality third glass substrates obtained through the thirddivision process may be glass substrates for middle-sized LCDs, and thegood-quality fourth glass substrates obtained through the fourth cuttingprocess may be glass substrates for small-sized LCDs. According tocircumstances, the third glass substrates may be half-finished productsused to manufacture the fourth glass substrates as the finishedproducts. Similarly, the second glass substrates may be half-finishedproducts used to manufacture the third glass substrates and/or thefourth glass substrates as the finished products.

For example, the first cutter may be moved to a portion of the glasssheet at which few defects are distributed in the length direction (‘Xdirection’) to cut the glass sheet into the first glass substrates.

For example, the second cutter may cut each of the first glasssubstrates into second glass substrates having no defects when each ofthe first glass substrates has no defects.

For example, the third cutter may cut each of the second glasssubstrates into a third glass substrate having defects and a third glasssubstrate having no defects when each of the second glass substrates hasdefects.

For example, the fourth cutter may cut the third glass substrate havingdefects to remove the defects from the third glass substrate.

The glass sheet manufacturing method may further include an arrangementprocess of performing mixed integer linear programming after performingthe inspection process to imaginarily arrange glass substrates on theglass sheet.

In this case, the restrictive expression of the mixed integer linearprogramming may include X, Y, Z coordinates of defects, the kind andsize of the glass substrate, and the size of the glass sheet, and theobjective expression of the mixed integer linear programming may beconfigured to maximize space utilization of the glass substrate.

DESCRIPTION OF DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view showing the construction of a glass sheet cuttingdevice according to an embodiment of the present invention;

FIG. 2 is a view showing the arrangement of a glass sheet cutting deviceaccording to an embodiment of the present invention;

FIG. 3 is a vertical sectional view typically showing a defect inspectorof FIG. 2;

FIG. 4 is a vertical sectional view taken along line A-A′ of FIG. 2;

FIG. 5 is a flow chart showing a glass sheet manufacturing methodaccording to an embodiment of the present invention; and

FIGS. 6 and 7 are a graph and a typical plan view showing comparisonbetween illustrative examples of the present invention and a comparativeexample.

BEST MODE

Now, preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be noted,however, that the scope of the present invention is not limited by theillustrated embodiments.

FIG. 1 is a view typically showing the construction of a glass sheetcutting device according to an embodiment of the present invention.

Referring to FIG. 1, a glass sheet cutting device 100 includes cutters20, a defect inspector 40, a position adjuster 10 and a controller 30.

The cutters 20 cut a glass sheet into quadrangular glass substrates, andthe position adjuster 10 moves at least one of the cutters to a portionof the glass sheet at which few defects are distributed.

The defect inspector 40 scans the glass sheet to three-dimensionallycheck defect positions of the glass sheet in the length direction, thewidth direction and the thickness direction of the glass sheet.

Also, the defect inspector 40 transmits scanned results, i.e.information on the defect positions indicated by an X coordinate, Ycoordinate and X coordinate, to the controller 30.

The defect inspector 40 captures the shapes of defects using cameras todetermine whether the defects are located inside or outside the glasssheet.

The controller 30 informs the position adjuster 10 of positions of thecutters 20 based on the scanned results received from the defectinspector 40 and divides the defects received from the defect inspector40 into a defect necessary to be repaired, a defect having goodconditions, a defect having poor conditions and a defect havingconditions that are difficult to determine.

Also, the controller 30 includes an arrangement server (not shown) forperforming mixed integer linear programming based on positionalinformation of the defects input by the defect inspector 40 toimaginarily arrange glass substrates on the glass sheet.

FIG. 2 is a view typically showing the arrangement of a glass sheetcutting device according to an embodiment of the present invention. FIG.3 is a vertical sectional view typically showing a defect inspector ofFIG. 2. Also, FIG. 4 is a vertical sectional view taken along line A-A′of FIG. 2.

Referring to these drawings, a glass sheet cutting device 102, which isa device for cutting a glass sheet 10, continuously supplied after amelting and solidification process, into quadrangular glass substrates14 and 18, includes four cutters 22, 24, 26 and 28 including positionadjusters, a defect inspector 42, a thickness inspector 44 and acontroller (not shown).

The cutters 22, 24, 26 and 28 include a first cutter 22 to cut the glasssheet 10 in the width direction (‘Y direction’) into first glasssubstrates 12, a second cutter 24 to cut each of the first glasssubstrates 12 in the length direction (‘X direction’) into second glasssubstrates 14, a third cutter 26 to cut each of the second glasssubstrates 14 in the width direction (‘X direction’) into third glasssubstrates 15 and 16, and a fourth cutter 28 to cut the third glasssubstrates 15 and 16 in the length direction (‘Y direction’).

Also, the first cutter 22 cuts the glass sheet 10 into first glasssubstrates 12 at the same intervals irrespective of defect positions,and the second cutter 24 cuts each of the first glass substrates 12 intosecond glass substrates 14 having no defects when each of the firstglass substrates 12 has no defects.

The third cutter 26 cuts each of the second glass substrates 14 into athird glass substrate 15 having defects and a third glass substrate 17having no defects when each of the second glass substrates 14 hasdefects. The fourth cutter 28 cuts the third glass substrate 15 toremove defects from the third glass substrate 15.

Also, the fourth cutter 28 cuts the third glass substrate 15 from oneend of the third glass substrate 15 within a range of less than 20% ofthe length L of the third glass substrate 15 to remove defects from thethird glass substrate 15.

Among the third glass substrates 15, 16 and 17, the defective glasssubstrate 16 having defects located at a portion that cannot be removedby the fourth cutter 28 is destroyed. The width of the defective glasssubstrate 16 is 10% or less of the size of the third glass substrate 17having no defects to minimize the size of the defective glass substrate16, which will be destroyed.

The defect inspector 42 is disposed ahead of the first cutter 22 in thelength direction X of the glass sheet 10. The defect inspector 42includes four or more cameras 46 to check defect positions of the glasssheet 10 in the length direction, the width direction and the thicknessdirection of the glass sheet 10.

The respective cameras 46 measure distances b and b′ and angles a and a′between the respective cameras and defects 52, 54 and 56 to check thedefect positions.

The defects 52, 54 and 56 include defects 52 and 54 located at the topand bottom of the glass sheet 10 and a defect 56 located in the glasssheet 10. The defects 52 and 54 located at the top and bottom of theglass sheet 10 are removed in a grinding process, as a post processingprocess. Consequently, the defects 52 and 54 are excluded from objectsto be cut.

The thickness inspector 44 is positioned between the defect inspector 44and the first cutter 22 to check unevenness of the outer surface of theglass sheet 10. If uneven portions 57 and 58 formed at the outer surfaceof the glass sheet 10 occupies, for example, 1% or more of the thicknessof the glass sheet 10, i.e. the uneven portions are defects that can beremoved in the grinding process, which is the post processing process,the defects are removed from the glass sheet 10.

Meanwhile, the glass sheet cutting device 102 includes a firstproduction line 32 to produce relatively large second glass substrates14, from which defects have been removed, and a second production line34 to produce relatively small fourth glass substrates 18, from whichdefects have been removed.

Also, the second production line 34 diverges from the first productionline 32.

FIG. 5 is a flow chart typically showing a glass sheet manufacturingmethod according to an embodiment of the present invention.

Referring to FIG. 5 together with FIGS. 2 and 3, the glass sheetmanufacturing method, which is a method of manufacturing quadrangularglass substrates 14 and 18 from a glass sheet 10, which is continuouslysupplied after a melting and solidification process, includes aninspection process (S10) of scanning the glass sheet 10 using the defectinspector 42 to three-dimensionally check the positions of defects 52,54 and 56 in the length direction, the width direction and the thicknessdirection of the glass sheet 10, a first division process (S20) ofcutting the glass sheet 10 in the width direction (‘X direction’) usingthe first cutter 22 to divide the glass sheet 10 into first glasssubstrates 12, a second division process (S30) of cutting each of thefirst glass substrates 12 in the length direction (‘Y direction’) usingthe second cutter 24 to divide each of the first glass substrates 12into second glass substrates 14, a third division process (S40) ofcutting each of the second glass substrates 14 in the width direction(‘X direction’) using the third cutter 26 to divide each of the secondglass substrates 14 into third glass substrates 15, a fourth cuttingprocess (S50) of cutting each of the third glass substrates 15 in thelength direction (‘Y direction’) using the fourth cutter 28, and a postprocessing process (S60) of grinding the surfaces of glass substratesobtained in the fourth cutting process (S50) to remove defects that havebeen sorted as ones that can be removed in the inspection process (S10).

Also, the first cutter 22 cuts the glass sheet 10 into first glasssubstrates 12 at the same intervals irrespective of defect positions,and the second cutter 24 cuts each of the first glass substrates 12 intosecond glass substrates 14 having no defects when each of the firstglass substrates 12 has no defects.

The third cutter 26 cuts each of the second glass substrates 14 into athird glass substrate 15 having defects and a third glass substrate 17having no defects when each of the second glass substrates 14 hasdefects. The fourth cutter 28 cuts the third glass substrate 15 toremove defects from the third glass substrate 15.

Hereinafter, the present invention will be described in more detailbased on experiments; however, the following experiments are given onlyto illustrate the present invention, and therefore, the scope of thepresent invention is not limited to the experiments.

EXAMPLE 1

Mixed integer linear programming was performed in consideration of thesize of glass substrates for A type liquid crystal displays (LCDs) toarrange glass substrates for A type LCDs at positions having no defectson a glass sheet. In an objective expression of the mixed integer linearprogramming, the area efficiency of the glass substrates for A type LCDswas maximized. In a restrictive expression of the mixed integer linearprogramming, computer simulation was carried out using the size anddefect coordinates (X, Y, Z) of the glass substrates for A type LCDs.

EXAMPLE 2

The same method as in Example 1 was used except that the size of theglass substrates for B type LCDs, the size of which is half that of theglass substrates for A type LCDs was considered in an objectiveexpression of the mixed integer linear programming, and the areaefficiency of the glass substrates for B type LCDs was maximized in arestrictive expression of the mixed integer linear programming, in astate in which the glass substrates for A type LCDs were arranged on theglass sheet based on the results obtained in Example 1.

COMPARATIVE EXAMPLE 1

Glass substrates for A type LCDs were sequentially arranged on a glasssheet from the left end to the right end of the glass sheet in thelength direction of the glass sheet based on the size of the glasssubstrates for A type LCDs without using mixed integer linearprogramming

EXPERIMENTAL EXAMPLE 1

The cutting results based on the arrangement of the glass substratesperformed in the above examples and comparative example are shown inFIGS. 6 and 7.

First, referring to FIG. 6, it can be seen that yield of the glasssubstrates was decreased as the defect density of the glass substratesaccording to the examples and Comparative example 1 was increased, butthe yield of the glass substrates according to Examples 1 and 2 was moreslowly decreased than that of the glass substrates according toComparative example 1.

Subsequently, referring to FIG. 7 together with FIG. 6, it can be seenthat, when the defect density was 0.17, the yield of Comparative example1 was approximately 25%, the yield of Example 1 was approximately 43%,and the yield of Example 2 was approximately 69%. Consequently, it canbe seen that, when the glass sheet cutting device according to thepresent invention is used, yield is sharply increased with the resultthat it is possible to greatly reduce manufacturing costs.

Specifically, it can be seen that six good-quality glass substrates forA type LCDs were produced according to Comparative example 1, and sevengood-quality glass substrates for A type LCDs were produced according toExample 1. Also, it can be seen that seven good-quality glass substratesfor A type LCDs were produced and, at the same time, sixteengood-quality glass substrates for B type LCDs were produced according toExample 2.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

INDUSTRIAL APPLICABILITY

As is apparent from the above description, the glass sheet cuttingdevice according to the present invention is configured so that, when aglass sheet is cut into quadrangular glass substrates, the glass sheetis scanned using the defect inspector to three-dimensionally checkdefect positions in the length direction, the width direction and thethickness direction of the glass sheet, and at least one of the cuttersis moved to a portion of the glass sheet at which few defects aredistributed to manufacture a plurality of glass substrates.Consequently, it is possible to maximize yield of the glass substrates.

Also, the glass sheet is cut into at least two kinds of glasssubstrates. Consequently, it is possible to improve yield of the glasssubstrates, thereby greatly reducing manufacturing costs.

1. A device for cutting a glass sheet, continuously supplied after amelting and solidification process, into quadrangular glass substrates,the glass sheet cutting device comprising: two or more cutters forcutting a glass sheet into quadrangular glass substrates; a defectinspector for scanning the glass sheet to three-dimensionally checkdefect positions in a length direction, a width direction and athickness direction of the glass sheet; a position adjuster for movingat least one of the cutters to a portion of the glass sheet at which fewdefects are distributed; and a controller for informing the positionadjuster of positions of the cutters based on the scanned resultsreceived from the defect inspector.
 2. The glass sheet cutting deviceaccording to claim 1, wherein each of the cutters is a diamond knife ora light source for cutting.
 3. The glass sheet cutting device accordingto claim 2, wherein the light source for cutting is a laser.
 4. Theglass sheet cutting device according to claim 1, wherein the cutterscomprise: a first cutter for cutting the glass sheet in the widthdirection (‘Y direction’) into first glass substrates; a second cutterfor cutting each of the first glass substrates in the length direction(‘X direction’) into second glass substrates; a third cutter for cuttingeach of the second glass substrates in the width direction (‘Xdirection’) into third glass substrates; and a fourth cutter for cuttingthe third glass substrates in the length direction (‘Y direction’). 5.The glass sheet cutting device according to claim 4, wherein the firstcutter is moved to a portion of the glass sheet at which few defects aredistributed in the length direction (‘X direction’) to cut the glasssheet into the first glass substrates.
 6. The glass sheet cutting deviceaccording to claim 4, wherein the second cutter cuts each of the firstglass substrates into second glass substrates having no defects wheneach of the first glass substrates has no defects.
 7. The glass sheetcutting device according to claim 4, wherein the third cutter cuts eachof the second glass substrates into a third glass substrate havingdefects and a third glass substrate having no defects when each of thesecond glass substrates has defects.
 8. The glass sheet cutting deviceaccording to claim 4, wherein the fourth cutter cuts the third glasssubstrate having defects to remove the defects from the third glasssubstrate.
 9. The glass sheet cutting device according to claim 8,wherein the fourth cutter cuts the third glass substrate having defectsfrom one end or opposite ends of the third glass substrate within arange of less than 30% of a length of the third glass substrate toremove the defects from the third glass substrate.
 10. The glass sheetcutting device according to claim 7, wherein, among the third glasssubstrates, a defective glass substrate having defects located at aportion that cannot be removed by the fourth cutter is destroyed. 11.The glass sheet cutting device according to claim 10, wherein the widthof the defective glass substrate is 20% or less of the size of the glasssubstrate having no defects to minimize the size of the defective glasssubstrate.
 12. The glass sheet cutting device according to claim 1,wherein the defect inspector is disposed ahead of the cutters in thelength direction of the glass sheet.
 13. The glass sheet cutting deviceaccording to claim 1, wherein the defect inspector comprises two or morecameras for checking the defect positions of the glass sheet in thelength direction, the width direction and the thickness direction of theglass sheet.
 14. The glass sheet cutting device according to claim 13,wherein the cameras measure distances and angles between the camera andthe defect to check the defect positions.
 15. The glass sheet cuttingdevice according to claim 1, wherein the defects comprise fish eyes,bubbles, black dots, white dots, or protrusions or grooves formed at theouter surface of the glass sheet.
 16. The glass sheet cutting deviceaccording to claim 1, wherein the defects located at the outer surface,i.e. the top or bottom, of the glass sheet are excluded from objects tobe cut.
 17. The glass sheet cutting device according to claim 1, whereinthe controller comprises an arrangement server for performing mixedinteger linear programming based on positional information of thedefects input by the defect inspector to imaginarily arrange glasssubstrates on the glass sheet.
 18. The glass sheet cutting deviceaccording to claim 1, further comprising a thickness inspector forchecking unevenness of the outer surface of the glass sheet.
 19. Theglass sheet cutting device according to claim 18, wherein, if theunevenness of the outer surface of the glass sheet is 1% or more of thethickness of the glass sheet, the unevenness is regarded as defects tobe removed.
 20. The glass sheet cutting device according to claim 18,wherein the thickness inspector is positioned between the defectinspector and the cutters.
 21. The glass sheet cutting device accordingto claim 1, wherein each of the glass substrate is a glass panel forliquid crystal displays (LCDs), a glass panel for organic light emittingdiodes (OLEDs) or a glass panel for plasma display panels (PDPs). 22.The glass sheet cutting device according to claim 1, wherein the glasssheet cutting device comprises a first production line to producerelatively large glass substrates, from which defects have been removedand a second production line to produce relatively small glasssubstrates, from which defects have been removed.
 23. The glass sheetcutting device according to claim 22, wherein the second production linediverges from the first production line.
 24. A method of manufacturingquadrangular glass substrates from a glass sheet, which is continuouslysupplied after a melting and solidification process, the glass sheetmanufacturing method comprising: an inspection process of scanning theglass sheet using a defect inspector to three-dimensionally check thepositions of defects in a length direction, a width direction and athickness direction of the glass sheet; a first division process ofcutting the glass sheet in the width direction (‘X direction’) using afirst cutter to divide the glass sheet into first glass substrates; asecond division process of cutting each of the first glass substrates inthe length direction (‘Y direction’) using a second cutter to divideeach of the first glass substrates into second glass substrates; a thirddivision process of cutting each of the second glass substrates in thewidth direction (‘X direction’) using a third cutter to divide each ofthe second glass substrates into third glass substrates; a fourthcutting process of cutting each of the third glass substrates in thelength direction (‘Y direction’) using a fourth cutter; and a postprocessing process of grinding surfaces of glass substrates obtained inthe fourth cutting process to remove defects that have been sorted asones that can be removed in the inspection process.
 25. The glass sheetmanufacturing method according to claim 24, further comprising anarrangement process of performing mixed integer linear programming afterperforming the inspection process to imaginarily arrange glasssubstrates on the glass sheet.